In particular in the area of microlithography, apart from the use of components that are configured with the highest possible precision, among the desired properties are to set the position and geometry of optical modules of the imaging device, that is to say for example the modules with optical elements such as lenses, mirrors or gratings, but also the masks and substrates that are used, as precisely as possible according to predefined setpoint values during operation, or to stabilize such components in a predefined position or geometry in order to achieve a correspondingly high imaging quality.
In the area of microlithography, the accuracy requirements are in the microscopic range of the order of a few nanometers or below. They are in this case not least a consequence of the constant demand to increase the resolution of the optical systems that are used in the production of microelectronic circuits in order to advance the miniaturization of the microelectronic circuits to be produced.
With the increased resolution, and the generally accompanying reduction in the wavelength of the light used, the requirements for the accuracy of the positioning and orientation of the components used naturally increase. In particular for the low operating wavelengths that are used in microlithography in the UV range (for example in the range of 193 nm), but in particular in the so-called extreme UV range (EUV), with operating wavelengths between 5 nm and 20 nm (typically in the range of 13 nm), this of course has an effect on the effort that has to be expended to maintain the high requirements for the accuracy of the positioning and/or orientation of the components involved.
In particular in conjunction with the aforementioned EUV systems, refined influencing of the intensity distribution of the light that is used for the imaging is gaining ever increasing importance. For this purpose, generally so-called facet mirrors are used, in which a multiplicity of extremely small facet elements with an exactly defined position and/or orientation of their optically effective surface with respect to a predefinable reference are arranged in a grid that is as closely spaced as possible. It is in this respect often desired or required (e.g. for a change of the illumination setting) to change the alignment of the facet elements, consequently therefore to tilt their optical surface.
It is known from DE 102 05 425 A1 (Holderer et al.) and DE 10 2008 009 600 A1 (Dinger), the respective disclosure of which is incorporated herein by reference, in conjunction with the defined positioning and orientation of the facet elements of a facet mirror of an EUV system to adjust these facet elements individually. For this purpose, the facet elements are tilted about a tilting axis defined by the supporting structure via a corresponding tilting moment, which is exerted on the facet element by an assigned actuator unit.
In the case of some of the rotationally symmetric facet elements that are known from DE 102 05 425 A1, the tilting axis lies in the plane of main extension of the optical surface, with the tilting moment that is exerted by the actuator unit running parallel to the plane of main extension of the optical surface, and so the optical surface is just tilted, without the facet element undergoing any lateral displacement from the installation space that is provided for the facet element.
Because of the absence of lateral displacement during the tilting, the known facet elements can in principle be positioned particularly close to one another, and therefore do not require large gaps between the facet elements. It is problematic here however that the rotationally symmetric design itself causes comparatively low utilization of the surface area or comparatively large gaps between the facet elements, in which there may be a comparatively great loss of light.
To avoid such losses of light due to gaps between facet elements, or as a result of certain illumination settings, often elongate, non-rotationally symmetric facet elements, which in principle lie against one another almost without any gap in a certain alignment or in a certain switching state, are used. Such a configuration is known for example from DE 10 2008 009 600 A1, providing a cardanic support for the facet elements that has two orthogonal tilting axes which run parallel to the plane of the supporting structure of the facet elements.
A similar support for such elongate, non-rotationally symmetric facet elements is also known from DE 10 2012 223 034 A1 (Latzel et al.), the disclosure of which is incorporated herein by reference. There, the supporting of the respective facet element on a supporting structure is realized by way of a three-rod support in the manner of a ball joint, the optical surfaces of the facet elements running parallel to the plane of the supporting structure. The ball-joint-like support in this case defines an infinite number of tilting axes for the respective facet element, and so the actual tilting axis must then be predefined by the actuating mechanism. Here, too, the actuating mechanism again acts parallel to the plane of the supporting structure of the facet elements, and so the tilting moment that is exerted on the facet element lies in the optical surface. Therefore, here, too, the actuating mechanism consequently again provides tilting axes that run parallel to the plane of the supporting structure of the facet elements.
Certain settings require however that the planes of main extension of the optical surfaces of some (possibly even all) of the facet elements run in an inclined manner in relation to the plane of main extension of the base element of their supporting structure. Not least as a result of the existing restrictions with respect to installation space, this often means that the tilting moment produced by the actuating mechanism (in the region of the base element of its supporting structure) runs in an inclined manner in relation to the plane of main extension of the optical surface.
This inclination of the tilting moment in relation to the plane of main extension has the disadvantage that, apart from the desired component (producing the tilting of the optical surface) parallel to the plane of main extension, the tilting moment also has a parasitic component perpendicular to the plane of main extension, which brings with it an undesired rotation of the optical surface in the plane of main extension. Especially in the case of long, slender facet elements, this rotation of the optical surface in the plane of main extension leads to a greater or lesser degree of lateral displacement of the free ends of the facet elements, for which it is desirable to provide corresponding clearances between the facet elements that are undesired (from the aspect of the least possible loss of light).